Fluorescent lamps, that is, low-pressure discharge lamps, customarily use double-coiled or coiled-coil electrodes which are held in electrode mounts so as to be essentially rod or pin-like, located effectively transversely to the longitudinal axis of the usually elongated fluorescent lamp. Double-coiled or coiled-coil filaments are well known in lamp technologies. The double-coiled filaments are activated by being coated with a mixture of barium and strontium carbonate. It has been known to utilize such a mixture in which approximately equal values of strontium carbonate and barium carbonate are used. The emission values of such mixtures have been considered an optimum. An equimolar mixture of barium carbonate and strontium carbonate, to which approximately 10% of calcium carbonate is added, also gives good emission values after the electrodes have been activated. In the activation process, the carbonates are converted into corresponding metal oxides. Electrodes of this type are described in the referenced literature, "DIE OXYDKATHODE" ("THE OXIDE CATHODE"), Vol 2, by G. Herrmann and S. Wagener, Johann Ambrosius Barth, publishers, Leipzig, 2nd printing (1950), pages 25-33 and 137-138.
Emitter coating compositions as known can be used not only for fluorescent lamps with heated cathodes but can also be used for cold-start fluorescent lamps. Cold-start fluorescent lamps are lamps which do not require pre-heating of the electrode windings.
The electrode windings are extremely highly loaded upon cold-starting of fluorescent lamps when the lamps are energized, that is, upon initial ignition. First, a glow phase results, in which the electrode windings are subjected to an intense ion bombardment, leading to heating of the electrodes and formation of a hot spot or discharge spot on the electrode filament windings, from which, then, the transition to the arc discharge occurs. The ion bombardment results in damage to the electrode windings by sputtering-off of electrode material and emitter material. This sputtered-off material deposits or precipitates on the inner wall of the discharge envelope, typically an elongated, straight or bent tube, resulting in undesired blackening at the ends of the discharge envelope. Extended glow phases, further, may lead to premature breakage of the electrode winding, thus reducing the lifetime of the fluorescent lamp.